GB2362127A - Method and apparatus for controlling a tractor/baler combination - Google Patents

Abstract

In a tractor/baler combination, a method of controlling the combination includes the steps of: <SL> <LI>(i) advancing a tractor/baler combination through a swath or windrow of biological matter with the tractor PTO 28 operating at a generally constant speed to power the baler and the baler operating to take up biological matter; <LI>(ii) during step (i) assessing the flowrate of biological matter in the baler; <LI>(iii) comparing the assessed flowrate with an optimal flowrate; and <LI>(iv) if the assessed flowrate differs from the optimal flowrate by more than a predetermined amount, changing the speed of advancement of the tractor/baler combination, and hence changing the flowrate of biological matter in the baler. </SL> There is also disclosed an apparatus (10) for carrying out the method of the invention. The method and apparatus of the invention advantageously increase the workrate of baling operations.

Description

2362127 METHOD AND APPARATUS FOR CONTROLLING A TRACTOR/BALER COMBINATION

This invention relates to a method and apparatus for controlling a tractor/baler combination.

In the field of agricultural vehicles it is well known to provide a baler, that is towable behind a tractor, to gather and form into bales biological matter left after a harvesting or mowing operation.

"Biological matter" as used herein includes but is not limited to straw, grass, hay, forage and silage.

"Tractor" as used herein includes any vehicle capable of propelling and providing power to a baler.

A baler is in use hitched to the tractor hitch and draws power from the tractor power take off (PTO) shaft, for the purposes of gathering and compacting biological matter. The biological matter typically lies in swaths or windrows in a field. The baler gathers the biological matter, typically lying over a distance of several tens of metres, into an intake at the front of the baler. The baler compacts the biological matter into a bale of predetermined shape. The baler includes mechanisms for tying the bales with strong twine and knotting the twine; and then ejecting each completed bale, as it is formed, from the rear of the baler.

A development occurred in the baler art in the late 1970's. This was the introduction of so-called 1arge rectangular balers", or 9arge square balers". Some known large rectangular balers are capable of producing cuboidal bales each weighing a tonne or more. This represented a 1 significant increase, in baling capacity, over the previously available balers.

However it is becoming increasingly common for operators to use soS called "Midi" balers that typically produce bale masses in the range 250750 kg. The invention is particularly but not exclusively suitable for use in such Midi-balers.

During use the precompression chamber forming part of a rectangular 10 baler periodically transfers biological matter to a main baling chamber. A piston, in the baling chamber, that reciprocates under power from the tractor PTO shaft, compresses the biological material into a bale whose density is dictated by numerous factors including the volume of each charge from the precompression chamber.

Rectangular balers operate most efficiently when the swaths of biological material through which they are towed are of constant density. This ensures that the precompression chamber fills at a substantially constant rate.

In practical use of large rectangular balers, however, the swath density is rarely constant over an entire field, or even from place to place in a swath.

This can be for a number of reasons, including variations in crop density before harvesting; and variations in efficiency of the harvesting process leaving different amounts of biological material in different parts of the swaths. Such variations in the swaths often arise when, during harvesting, a harvesting machine (typically a combine harvester) has to slow down or stop part way along a row of crop. The variations also 2 arise at junctions between swaths, in non-rectangular fields.

Hitherto the operator of a tractor/baler combination has had to rely on visual inspection of the swaths as the tractor approached them, in order to judge the swath density. If the operator perceived a region of low swath density he would attempt to increase the tractor forward speed to try and temporarily increase the rate of intake of biological material into the precompression chamber, with the aim of maintaining a generally constant throughput of biological material through the baler.

Similarly if the operator noticed a region of high density in the swath he would attempt to reduce the tractor speed by an appropriate amount.

This method of regulating the throughput of biological material is 15 inefficient for numerous reasons, including:

A lack of consistency in the remedial action taken to overcome low and high bale densities.

The possibility of overloading the tractor engine when attempting to accelerate the tractor, eg. as a result of performing transmission shifts that are not timed correctly and hence coincide with peak PTO shaft loadings. This can have an adverse effect on the engine loading and can in any event cause the tractor to slow or stop, 25 thereby affecting workrate.

Failure to notice or respond adequately to high swath densities leading to blockages, in the precompression chamber, that require halting of the baling operation to clear.

3 The tractor operator taking remedial action for too long or too short a period.

In sloping fields the above-noted problems are frequently more acute than 5 in flat fields.

In general it is desirable to maximise workrate during baling operations. One reason for this is that the moisture content of the biological material frequently affects its specific mass, quality and value. It is likely that delays and inefficiencies in baling operations will allow unacceptable moisture content changes, especially in countries, such as those in Northern Europe, whose climates are variable at most times of year.

The prior art discloses several attempts at improving the consistency of the charge supplied from the precompression chamber to the baling chamber.

In GB 1 575 243 and US 4,034,543 mechanisms temporarily halt both the baling plunger and the stuffer fork that supplies charges of biological material from the precompression chamber, when a mass sensor detects underloading of the said chamber.

However, US 4,135,444 notes that the technique of GB 1 575 243 and US 4, 034,543 is sub-optimal because the need to accelerate and decelerate the massive plunger leads to failure of mechanical components, such as clutches, in the baler.

US 4,135,444 proposes temporary halting of only the stuffer forks, while the plunger continues to reciprocate, until the charge in the precompression chamber is adequate.

4 However there is no. disclosure in US 4,135,444 of how to accommodate swaths of high density, that lead to overloading of the precompression chamber and/or the tractor engine.

Also, none of the aforementioned documents discloses an apparatus or method whose aim is to maximise the overall workrate of the tractor/baler combination; nor does any of them disclose a method or apparatus that may compensate for the effects of field slope on baler throughput.

Claims (1)

1. According to the invention in a first aspect there is provided a method

   according to Claim 1.

   The step of comparing the assessed flowrate against an optimal flowrate, and adjusting the tractor speed in dependence on the outcome of the comparison, advantageously ensures that the tractor speed is changed only when necessary, as determined by the assessed flowrate of biological material.

   The method of the invention advantageously adjusts the flowrate, by adjusting the tractor forward speed, both when the flowrate of material through the baler is too high; and when the flowrate is too low.

   The method of the invention thus optimises flowrate and prevents blocking of the precompression chamber.

   If the method steps are repeated cyclically, eg. in dependence on the pulses of the clock of a microprocessor arranged to carry out the method, the correction effected by adjustment of the vehicle speed may take effect only for the duration of the sub-optimal flowrate through the baler.

   Preferably the step of changing the speed of advancement of the tractor/baler comb ination is as defined in Claim 2.

   Using transmission shifts to change the vehicle speed allows the tractor engine to run at constant speed, in a manner described hereinbelow. This advantageously ensures that the PTO shaft speed does not vary significantly while the speed change takes place.

   Also, as described hereinbelow, the use of transmission shifts permits method steps that minimise the risk of overloading or over-revving the tractor engine.

   Conveniently the method is as defined in Claim 3. This allows the 15 method to tolerate minor variations in the flowrate of biological material, without the need for the tractor transmission ratio to shift incessantly.

   The method preferably maintains the engine speed generally constant during advancing of the tractor/baler combination. Consequently the method may advantageously be carried out by or in conjunction with an apparatus as disclosed in published patent application number EP 0 838 141. The engine speed preferably is that required to give the correct, constant rotational speed of the PTO shaft to operate the baler.

   In a preferred method according to the invention, the step of assessing the flowrate of biological material is as defined in Clahn 5. As described in more detail below, each of the variables defined in Claim 5 is an acceptable indicator of the mass flowrate of biological material through the baler.

   6 The method of the invention preferably includes the steps defined in Claim 6.

   Predicting the tractor engine load and checking that it is less than a limit 5 value (as specified in Claim 6) before incrementing the transmission advantageously allows prevention of engine overloads on ratio change-up. This is particularly useful eg. when the tractor/baler combination is travelling uphill. At such times an increase in baler workrate that might, on level ground, be well within the engine capacity may in the absence of the Claim 6 step result in engine overloading resulting from the component of the tractor/baler mass acting down the slope.

   The prediction step is defined more specifically in Claim 7. Use of a reference model allows the use of a microprocessor in carrying out the prediction. The reference model is in particularly preferred embodiments stored as one. or more lookup tables in a memory forming part of or operatively connected to the microprocessor.

   A particularly preferred step for assessing the engine torque is defined in 20 Claim 8. This advantageously allows the use of a flywheel torque sensor as disclosed in patent number US 5,596,153.

   In preferred embodiments of the method the step of predicting the load on the tractor engine is carried out a plurality of times, as defined in Claim 9.

   This advantageously allows for the elimination of misleading instantaneous loadings that may otherwise cause unnecessary transmission shifts. Also, of course, repetitive sampling of the mass flowrate and predicted load conveniently suits the method to being carried out by or with the aid of a clock pulsed microprocessor.

   7 Optionally the method of the invention includes the features defined in Claim 10. These conveniently avoid overloading of the tractor engine as a result of increased swath density.

   More specifically the method is preferably as defined in Claim 11, the features of which, in a similar way to the Claim 9 features, permit the method, or any software and hardware implementing the method, to disregard misleading instantaneous mass flowrate values.

   A particularly preferred embodiment of the method is as defined in Claim 12. The features defined therein allow the decrementing of the transmission ratio more rapidly, if the assessed mass flowrate is greatly excessive (ie. greater than the optimal flowrate by at least the further predetermined amount), than if the assessed mass flowrate is greater than the optimal flowrate by a lesser amount (ie. the second predetermined amount defined in Claim 12). This conveniently avoids eg. the somewhat extreme form of tractor engine overload, that can cause plugging of the precompression chamber and/or shearing of a shear bolt, commonly present in balers, to protect the drive train for the stuffer forks.

   Conveniently the incrementing and decrementing of the transmission ratios, referred to herein, takes place when the reciprocably moveable baler plunger occupies a predetermined position. In preferred embodiments of the method of the invention the predetermined plunger position is chosen to avoid superimposing the torque loading arising from the gear change onto the peak loading from the plunger cycle. In one baler this is when the baler crank is between 130'-185' from its front dead centre (fdc) position. This notation relates to the position of the plunger in the bale chamber, as follows:

   8 00 = Plunger Fully Forward (Front Dead Centre) 1800 = Plunger Fully Rearward (Rear Dead Centre) Preferably the method is co-ordinated and/or carried out by or with the aid of one or more electronic processors such as a microprocessor, connected as defined in Claim 14.

   In particularly preferred embodiments the processor may form part of or be operatively connected to an apparatus as disclosed in EP-A-0 838 141.

   It is also preferable that the processor functions as defined in Claim 15. This feature advantageously allows the signals processed by the microprocessor to be substantially or entirely independent of the bale density. The bale density is in many balers variable either automatically (ie. under control of a bale density controller) or in dependence on a bale density setting that is adjustable by the tractor operator. It has been found that the PTO shaft torque is for some plunger positions in the plunger cycle dependent on the bale density and for other plunger positions substantially independent of the bale density. The feature of Claim 15 advantageously allows measuring of the PTO shaft torque when the plunger position corresponds to density-independent PTO shaft torque values.

   In any event it is advantageous to be able to time the sampling of each of the other parameters (selected from baler packer or rotary feeder. driveshaft torque; baler packer conrod force; and sensor door position) that may additionally be used to provide inputs to the control software that preferably carried out the method of the invention. One reason for this is that at certain points in the movement cycle of the plunger the at least one of the aforesaid parameters correlates more closely with the flowrate of 9 biological material, than at other points in the plunger cycle.

   Preferably the electronic processor operates, in accordance with the method of the invention, in the manner defined in Claim 16.

   The electronic processor optionally maintains the tractor engine speed generally constant, regardless of the engine loading, as defined in Claim 17. This may be achieved by means of the processor controlling the tractor engine governor.

   Further, advantageous features of the method when co-ordinated by a programinable processor are defined in Claims 18 and 19.

   According to a second aspect. of the invention there is provided a 15 tractor/baler combination as defined in Claim 21.

   The tractor/baler combination of the invention advantageously is suited to practising of the method of the first aspect of the invention.

   Conveniently the tractor/baler combination is as defined in Claims 22 to 33.

   The various stored values preferably are stored in the form of lookup tables in a memory device, such as the RAM of a microprocessor.

   Preferably the programmable device includes or is operatively connected to a memory having stored therein a steady state reference model that is as defined in Claim 33.

   There now follows a description of preferred embodiments of the invention, by way of non-limiting example, with reference being made to the accompanying drawings in which:

   Figures la-1d are schematic, side elevational views showing the 5 operating principles of a per se known, large rectangular baler including a plurality of packer forks for charging the precompressing chamber; Figure 2 shows the operating principles of another per se known baler having a rotary feeder mechanism in conjunction with a series of cutter knives; Figure 3 is a schematic, side Clevational view of a tractor/baler combination according to the invention; Figure 4 is a flow chart summarising the steps of a method according to the invention; Figure 5 is a graph of baler workrate vs swath density, in respect of is a tractor/baler combination according to the invention; Figure 6 is a functional block diagram of a steady state reference model forming part of the apparatus, and used in the method, of the invention; Figures 7 and 8 are graphical representations of outputs of the reference model of Figure 6; and Figures 9 and 10 show parts of the reference model of Figure 6 in more detail.

   Figures la-1b show the operation of a per se known baler 10 (Figure 3) 25 that may be towed behind a tractor 11 (Figure 3) as part of a tractor/baler combination.

   Towing of the baler 10 along a swath 12 of biological matter 15 causes its advancement such that the baler 10 takes up the biological matter 15.

   11 This is achieved by the combined actions of a continuously rotating pick up bar 13 and continuously rotating auger 14. Pick up bar includes a series of tines 16 that gather the biological matter 15 towards auger 14. The screws of auger 14 are arranged to drive the biological matter 15 to 5 the lateral mid-point of the baler intake area, and from there into a chute 17.

   The intake area of baler 10 may also optionally include a series of knife blades that are switchably operable to cut the pieces of biological matter to a predetermined size. It has been found through experimentation that the operation of the knife blades makes little appreciable difference to the mass flowrate of biological matter 15 through the baler.

   In chute 17 a series of packer forks 18 are driven by a drive shaft 20 to reciprocate continuously, by means of a four bar linkage arrangement indicated by numeral 20a, as indicated by the arrows A in Figure la. The packer forks 18 linkage biological matter 15 into a precompression chamber 19. Four bar chain 20a includes a pair of conrods 20b that drive the packer forks 18. A series of haydogs 21 are initially in an advanced position inserted into the upper end of precompression chamber 19 as shown in Figures. la and lb. The haydogs 21 prevent the biological matter 15 from advancing beyond the open end 19a of precompression chamber 19. Consequently the combined action of the packer forks, during the period depicted in Figures la and lb, fills the precompression chamber with biological matter 15.

   As an alternative to the packer forks 18 driven by a four bar linkage, some balers employ a rotary feeder mechanism as shown in Figure 2.

   The packer forks 18 and four bar mechanism 20a are absent from the 12 Figure 2 arrangement. The function of these components is carried out by a rotatable cylinder 150 having disposed extending along its outer surface, at four locations that are equi-spaced from one another, four series of feeder tines 151154. In practice the tines 151-154 extend as four angularly spaced helices.

   Cylinder 150 is rotatably supported on a shaft shown schematically by axis 155 extending transversely across the intake to precompression chamber 19. Thus rotation of cylinder 150, as a result of per se known io connection to a powered, rotatable drive shaft, in the direction of arrow X, causes feeding of biological material into precompression chamber 19.

   The operation of cylinder 150 is broadly similar to that of packer forks 18, but cylinder 150 gives rise to a more steady throughput that causes less pronounced peaks in the tractor power take off requirement.

   When the tine helices are defined by a series of laminae extending longitudinally along cylinder 150 the tines 151-154 may be rotationally interdigitated with a series of knives one (157) of which is visible in Figure 2. The knives function to crop pieces of the biological material to a predetermined length. Optionally the knives are retractible from the intake, under control of a retraction mechanism 15 8 that is known per se.

   Figure 2 omits the haydogs 21 for clarity, but of course these would normally be present.

   The precompression chamber 19 includes in its lower wall, near the packer forks 18 or rotary feeder, a sensor door 22. Sensor door 22 is spring biassed to a closed position flush with or protruding into the lower wall of precompression chamber 19, but when the mass of biological 13 matter 15 exceeds the biassing force maintaining the sensor door 22 closed, sensor door 22 opens as shown in Figure lb to trigger the next phase of operation of the baler 10, as shown in Figures lc and ld.

   The biassing force acting on sensor door 22 is equivalent to the mass of a predetermined charge of biological matter 15 in precompression chamber 19. In some balers the biassing force is adjustable, to take account of variations eg. in crop type and moisture content.

   Following opening of the sensor door 22 the haydogs 21 are withdrawn from the precompression chamber 19. Simultaneously a series of stuffer forks 23 enter the precompression chamber 19 to drive the charge of biological matter 15 out of upper, open end 19a of precompression chamber 19 and into a baling chamber 24. These operations are denoted by dotted arrows in Figure Ic.

   The stuffer forks 23 are omitted from Figure 2 for clarity, but would normally be present.

   A massive plunger 26 reciprocates continuously (eg. at 42 cycles per minute) along the length of baling chamber 24, to compact each charge of biological matter therein. Each cycle of operation of the components in the precompression chamber 19 results in the compaction of a charge that is a proportion of the mass of a completed bale. At the end of the baling chamber remote from the components shown in Figures la-ld, various sensors detect the completion of a bale and activate a tying and knotting mechanism that ties the bale with twine, before ejecting the completed bale from the rear of baler 10.

   During this process, as illustrated in Figure Id, the stuffer forks 23 14 withdraw from the upper end of precompression chamber 19; the haydogs 21 are reinserted into the precompression chamber 19; and the sensor door 22 is reset to its closed position to permit accumulation of a further charge of biological material.

   The operation of the stuffer forks 23 is timed with reciprocation of the plunger 26 since for much of its reciprocation the underside of plunger 26 closes the open end 19a of chamber 19. Clearly the stuffer forks 23 can only feed a charge into baling chamber 24 when the plunger 26 is at the extreme left hand end of its travel as shown in Figure 1.

   Referring now to Figure 3, a tractor/baler combination according to the invention includes a tractor 11 towing a baler 10 whose operation is essentially as shown in Figures la-ld or as modified by the Figure 2 arrangement.

   Baler 10 is attached by means of a drawbar 27 to the hitch of the tractor. PTO shaft 28 of tractor 11 rotates at constant speed to power the baler 10.

   Tractor 11 and baler 10 include a series of electronic processors in the form of microprocessors 29 that are, in the embodiment shown, connected to one another by means of a CAN-B US 31 or any equivalent means of electronic communication.

   The microprocessors 29 are in the Figure 3 embodiment present in part to constitute a vehicle control apparatus of the kind disclosed in EP-A-0 838 141. Clearly the functions of the control apparatus of EP-A-0 838 141, while highly desirable, are not essential for carrying out the invention disclosed herein. Consequently it is possible to devise working embodiments of the invention having more or fewer microprocessors 29 than those shown in Figure 3. Regardless of the microprocessor arrangement, embodiments of the invention include automatic control of the tractor engine speed and power output, preferably by means of one o f the microprocessors 29.

   Also regardless of the precise microprocessor arrangement, the tractor/baler combination of Figure 3 includes sensors detecting one or more of the torque in baler packer driveshaft 20; the torque in tractor PTO shaft 28; the force exerted by one or more of the baler packer fork 10 conrod 20b; and the position of sensor door 22.

   When the baler is of the type that includes a rotary feeder assembly, such as that exemplified by Figure 2, the packer conrod force would not be measured. Instead the rotary feeder driveshaft torque is used to provide 15 an indication of the loading deriving from the packing/feeding operation.

   Each of the above-noted variables has been found to correlate with the flowrate of biological material through the precompression chamber 19.

   Use of the sensor door position is advantageous because, if measured at a predetermined point in the plunger cycle, it is effectively a direct measure of the precompression chamber refill rate, that is the flowrate of biological material through the baler.

   The measured flowrate signal obtained fromthe sensor door position is independent of the bale density (that varies automatically in some balers). Consequently the sensor door position parameter is comparatively straightforward to employ, requiring a simple position sensor such as an LVDT, and a minimal amount of processing that is concerned primarily 30 with co-ordinating the sampling times with the plunger position.

   16 In contrast, the PTO torque value varies significantly in dependence on the bale density, at some points in the plunger cycle. However at other points in the plunger cycle the PTO shaft torque is substantially independent of bale density but nonetheless indicative of flowrate of biological material. Use of the PTO shaft torque as a control parameter therefore also requires a timing operation related to the plunger position.

   When using the PTO shaft torque as a parameter one has the choice 10 whether to locate the transducer on the baler or on the tractor that tows the baler.

   Clearly when the torque transducer is located on the tractor it is necessary to transmit data on the plunger position from the baler to the tractor in order to time the sampling of the torque measurements correctly. It may be impractical in such circumstances to use a hard wired connection between the baler and the tractor, so a transmitter/receiver combination would be necessary. Such apparatus, although readily realisable within the scope of the invention, requires additional processing power to ensure coding of data from the baler and eliminate the effects of transmission delays etc.

   The relationship between sensor door position and flowrate is a quadratic equation; whereas the relationship between PTO shaft torque and flowrate is linear. Thus the signal processing of the PTO shaft torque data is perhaps slightly simpler to carry out than that of the door position data.

   The packer shaft torque and packer conrod force values are also linearly related to the flowrate value.

   17 In the embodiment shown the baler packer driveshaft torque may be detected using a torque sensor in the form of a strain gauge forming part of a bridge circuit, and being operatively connected to a telemetry unit or via slip rings if so desired. These components are represented 5 schematically by numeral 32 in Figure 1 c, and are known per se.

   The PTO shaft torque may be detected eg. using a per se known torque sensor 33 shown schematically in Figure 3. When necessary the rotor feeder shaft torque could be detected using an analogous arrangement.

   The packer fork conrod force maybe measured by means of a further strain gauge 34 forming part of a bridge circuit, operatively connectable to one or more of the microprocessors 29.

   The sensor door position may be measured by means of a linear variable differential transformer (LVDT) 36 shown schematically in Figure 1c.

   In a practical embodiment of the invention, while sensor 33 is always present, only one of the sensors 32, 34 and 36 need be present. Sensor 36 20 is the simplest, cheapest and most convenient.

   The sensors 32, 33, 34 and 36 may each take a form other than the exemplary form described. Such variations are within the scope of the invention.

   The baler 10 includes a proximity sensor (not visible in the drawings but of per se known design) for detecting the true position of the baler plunger crank, and hence the actual plunger position.

   The tractor 11 includes a sensor detecting the transmission ratio of the 18 tractor transmission. In the embodiment shown the sensor may include one or more transducers operatively connecte to a transmission controlling microprocessor 29', but in embodiments lacking microprocessor 29' another arrangement may exist. For example the S transmission ratio transducer output(s) may feed directly to a single control processor.

   Optionally the tractor 11 also includes a sensor detecting the engine torque. When present this sensor may be eg. a flywheel torque sensor as disclosed in US 5,596,153.

   The microprocessor(s) 29 is/are programmed to implement a method described hereinbelow.

   The microprocessor(s) 29 is/are operatively connected to a memory having stored therein for comparison purposes:

   One or more optimal values of the mass flowrate of biological material flowing through the precompression chamber 19; the predetermined amounts referred to hereinbelow; the predetermined maxima referred to hereinbelow; and data representative of a predetermined position of the baler plunger.

   The following description of use of the apparatus of the invention, in accordance with the method of the invention, makes reference primarily to the flow diagram of Figure 4.

   In the following description reference is made to assessment of the flowrate of biological material by measurement of the position of sensor door 22 at certain points in the plunger cycle using LVDT 36. This is 19 because experiments indicate a close correlation, at certain points in the plunger cycle, between the sensor door position and the mass flowrate. However, as indicated above, any of the packer driveshaft torque, the rotary feeder driveshaft torque and the packer fork conrod force may equally well be used for this purpose, and terms descriptive of such data may be substituted into the following description in place of references to the sensor door position.

   In use of the apparatus of the invention the tractor/baler combination 11/10 commences advancing (step 50 of Figure 4) along a swath 12 of biological material 15. The swath may be of inhomogeneous density.

   During this action the tractor PTO shaft 28 rotates at constant speed. In practice this is achieved through one of the microprocessors 29" controlling the governor of the tractor engine in a per se known manner.

   The baler 10 takes up biological material 15 as described herein in relation to Figures la-1d and 2, while the tractor/baler combination advances.

   During operation of the combination 11110, control software programmed in the microprocessor(s) 29 assesses the mass flowrate of biological material 15 through the baler (steps 51-53).

   At the same thne the software preferably also measures (at step 51) the PTO torque and, when an appropriate sensor is present, the engine torque.

   The assessed mass flowrate value (step 51) is compared against an optimal flowrate, by assessing initially whether (step 52) the sensor door position is overloaded (ie. it exceeds a predetermined maximum position value, represented eg. by a particular voltage level in the signal from LVDT 36).

   If the result of the comparison at step 52 indicates overload of the sensor door position the control logic passes to step 59 that is concerned with decrementing the tractor transmission ratio; whereas if the comparison at step 52 indicates no overload of the sensor door position the control logic passes to step 53, that initiates an assessment of whether to increment the transmission ratio.

   Thus, regardless of the outcome of the comparison at step 52, the method includes the step of changing the speed of advancement of the combination 11110 (by changing the transmission ratio) and hence, since more or less biological matter 15 per unit time will enter the baler as a result, changing the mass flowrate of biological material through the baler.

   Step 53 therefore is a comparison of whether the assessed (actual) mass flowrate, determined from the LVDT signal, is less than the stored, optimal flowrate by more than a first, predetermined amount.

   At step 53 if the LVDT signal indicates the sensor door 22 position value to be less than its limit position, as stored in the memory device, corresponding to underloading of the precompression chamber 19, the microprocessor 29 predicts (step 54) what would be the engine load' were the software to increment the transmission ratio by one ratio step.

   The software then assesses, at step 55, whether the thus predicted load exceeds a predetermined value referred to as an "inhibit gear change set point". The point of steps 54 and 55 is to maintain the workrate of the baler, as determined from the position of sensor door 22, at greater than a predetermined minimum without causing overloading of the tractor 21 engine.

   The comparison at step 55 takes place with respect to data, that may be obtained through experimentation, that are stored in a memory (eg. ROM) operatively connected to the microprocessor 29.

   Figure 5 is one way of showing these data in graphical form. Figure 5 is a series of plots of baler workrate against swath density for each of six tractor transmission ratios measured when the tractor 11 of the combination of the invention travels on level ground. Of course tractors usually possess many more than six transmission ratios, but only a limited number, such as the six plotted, is likely to be suitable for baling operations.

   The solid line 85 superimposed on the plots of Figure 5 represents the effect of the software program. Taking for example the plot for transmission ratio BI (the lowest ratio tested), it is theoretically possible to operate at swath densities as low as 1.5kg/m but the workrate then drops to 5.5 tonnes/hour, an unacceptably low level. Consequently the solid line 85 represents a software-imposed requirement to increment to ratio B2 whenthe swath density (as assessed by the mass flowrate) falls to about 4.5 kglm, corresponding to "inhibit gear change set point" 80 in Figure 4. When this point is reached the transmission ratio increments to ratio B2, with the result that workrate instantaneously rises, as illustrated by line 85, to 25 t/hr, corresponding to the workrate in ratio B2 at a swath density of 3.5 kg/m and a predetermined tractor engine speed suitable for providing the correct PTO shaft speed for baler 10. Similar considerations apply to subsequent "inhibit gear change set

   points" 81-84 corresponding to changes up respectively to ratios B3-B6.

   22 Thus in one baler the method ensures a workrate of between 21 and 25 t/hr, by incrementing the transmission ratio each time the swath density drops to 21 t/hr unless the prediction algorithm (step 52) indicates likely overloading of the tractor engine. Obviously different tractor/baler combinations can be configured to operate between different upper and lower workrate limits if desired. The workrate limits are also influenced by the prevailing field conditions.

   The graph of Figure 5, that preferably is specific to the tractor/baler 10 combination 11/10 under consideration, may be stored in ROM (eg. a CDROM) readable by the microprocess0r(s) 29. The tractor 11 and/or the baler 10 may for this purpose include or have operatively connected thereto a disc reader. The graph of Figure 5 may be in the form of a lookup table.

   If the result of the comparison at. step 55 is that the transmission ratio should increment, a flag (eg. a bit of data) is set at step 56 indicating the need for a change up.

   The software then loops and carries out steps 51-55 again, so that the step of predicting the tractor engine load is carried out a plurality of times.

   The transmission ratio increments only if a predetermined number, preferably four, successive p redictions indicates that the engine will not be overloaded, as represented by the comparison at step 57, which confirms whether four successive change up flags are set. If the result of the comparison at step 57 is a logic state 'I', the software calls a subroutine (step 58) that increments the transmission ratio, eg. using microprocessor 29' if present.

   23 The software then loops iteratively, thereby repeatedly assessing the need for transmission ratio shifts. In practice the software samples the mass flowrate once per cycle of plunger 26 (ie. about once every 1.4 seconds in a New Holland D1010 "Cropeutter" baler).

   If comparison 52 indicates that the sensor door position corresponding to mass flowrate, and optionally the PTO or engine, is overloaded, the control logic moves to step 59, that is a precursor to decrementing the transmission ratio. 10 Step 59 represents a comparison of the assessed flowrate (and, optionally, the PTO and engine loadings) against stored optimal values. If the flowrate is greater than the stored optimal value by a second predetermined amount that is less than a further predetermined amount, a 15 change down flag is set (step 60). At step 61 the number of successive change down flags that are set is counted, and if the number is less than a predetermined value (preferably four) loops the control logic back to step 51 to carry out a further assessment of whether the transmission ratio should decrement. Only when the predetermined number (eg. four, as 20 noted) of successive change down flags is set does the software call a ratio change down subroutine (step 62). The change down may be implemented eg. by microprocessor 29'. Preferably the comparison at step 59 makes use of the data shown 25 graphically in Figure 5 and stored in the vehicle ROM. In the case of the step 59 comparisons the mass flowrate, represented by the swath density (ie. x axis) values in Figure 5 is compared against an optimal (overload) value for the selected gear ratio. Thus in the case of gear B6, the optimal swath density value is represented by point 86 on line 85. If the actual 30 swath density exceeds 25 t/hr in ratio B6, subroutine 62 is called causing 24 a ratio decrement to gear B5. The control logic functions similarly for the optimal values 87-90 corresponding respectively to the ratio shifts to gears B4-Bl.

   If the comparison at block 59 indicates that the assessed mass flowrate is greater than optimal by more than a stored further predetermined amount, the logic bypasses step 62 in favour of step 63 that sets a so- called "fast change down" flag (eg. a bit in RAM). The software then functions as before except that, as indicated at step 64, it is necessary for a lesser number (eg. two) of successive fast change down flags to be set for the transmission to decrement by means of subroutine 62 as described above.

   The transmission changes are timed to coincide with a predetermined position in the reciprocal. movement of the Wer plunger. In the New is Holland P1010 "Cropcuttqr" baler this t when the baler crank is not 130'-185' from fdc.

   Although the method of the invention has been described in relation to software control of microprocessor functions, in turn controlling subsystems of the combination 11/10, the method may be implemented in other ways eg. using pneumatic or hydraulic control elements.

   In determining at step 55 (Figure 4) whether the relevant'inhibit change up set point would be exceeded, the software employs a steady state reference model, that may also be stored in ROM, to make the prediction. The reference model predicts the engine loading that would result if the proposed transmission shift were to be made, taking account of the values of various variables prevailing at the time of the prediction.

   Figure 6 shows the reference model in a schematic form, in which both linear and non-linear functions are represented by the rectangular blocks.

   The model, which incorporates mathematical representations of the subsystems described hereinabove, and the relationships derived from field :5 evaluation tests includes a main iterative loop 40 and a number of subroutines 41-44, 46 and 47.

   At start up, subroutine 41 represents one way of calculating a set of swath density values represented by block 41a, by multiplying a field density value, determined eg. from field measurements, by a combine header width value that is, in effect, a swath width value. A range of the resulting swath density values is thereby stored, so that the model may be parameterised according to the prevailing swath density for each operation.

   At startup, subroutine 42 calculates an initial value representative of the field slope, based on the output of an inclinometer on the tractor or baler and represented schematically by numeral 42a. The resulting field slope value 42b is used to allow for increases, in the overall loading on the tractor engine, resulting from operation of the tractor to pull a baler up an incline.

   At startup, subroutine 43 calculates an initial value 43a of engine speed at no load.

   Subroutine 44 increments from the lowest to the highest available gear ratio (within transmission limits), and enables the main loop to run with each new transmission ratio. Subroutine 44 thus permits calculation of the startup values at blocks 41-43 in each of a range of transmission ratios; and also permits operation of main loop 40 in each of the ratios of the 26 range.

   In a preferred form of the reference model main loop 40 calculates inter alia the sensor door position 40a, the PTO shaft torque 40b and the vehicle rolling resistance 40d using values generated by the startup subroutines 41-43. The results of the calculations in main loop 40 are plotted in a lookup table, represented graphically by graph 46a in output routine 46.

   The calculations carried out in main loop 40 preferably take place during one or more calibration runs of the tractor/baler combination, in the first few minutes or seconds of operation. Optionally the software may permit the tractor operator to select a calibration mode of operation at any time.

   Initially during the calibration run the control software selects the lowest transmission ratio of the range suitable for baling operations. Once the calibration is complete in that ratio the subroutine 44 increments the transmission ratio by one step. The calibration operation then repeats.

   This process repeats iteratively until the calibration is complete for all the transmission ratios that are suitable for baling operations. The result then is the series of plots represented graphically at 46a and 47a and shown in more detail in Figures 7 and 8. The Figure 7 and 8 plots are subsequently used, during operation of the baler, to determine the tractor/baler 25 workrate in dependence on the prevailing swath density.

   Figures 9 and 10 show respectively the calculation of the sensor door position and the PTO torque value at startup, as represented by blocks 40a and 40b in Figure 6.

   27 The relationship between the flowate of biological material and the sensor door position has been found experimentally to be expressed by:

   P= r, M2 +r2 m-cl....

   In which:

   P is the sensor door position expressed as a percentage of its range of possible movement; m is the flowrate of biological material in kg/s; cl is a constant; and r, and r2are coefficients.

   The actual values of cl, r, and r2 have been determined from field tr%s.

   is Figure 9 shows this expression in functional block form, as carried out at block 40a in subroutine 40 of Figure 6.

   Similarly the relationship between the PTO shaft torque and the flowrate of biological material may be expressed by:

   T = r, M-C2.... (2) In which:

   T is the PTO shaft torque in Nm; m is the flowrate of biological material in kgls; C2 is a constant; and r3 is a coefficient.

   28 The actual valuesOf C2and r3 have been determined from field trails.

   Although the relationships defining the variables are related by 5 expressions such as Equations (1) and (2) herein, the actual values used in the reference model may be in the form of pre-calculated values or may be calculated in real time on the basis Of outputs of the various sensors on the tractor/baler combination. In practice the model will contain a mixture of pre-calculated values such as parameters of the tractor/baler combination; and values that are calculated in dependence on instantaneously prevailing sensor values.

   Although the preferred form of the reference model is a steady state model, this does not mean that the model is invariant. On the contrary, the model is periodically updated (eg. once per a set number of clock pulses). Consequently each comparison with the reference model takes account of changes in the conditions under which the tractor/baler combination operates.

   As noted, one way of visualising the model outputs is in graphical form. The respective output graphs 46a and 47a of the subroutines 46 and 47 are shown enlarged as Figures 7 and 8.

   In operation the reference model predicts the workrate of the tractor and 25 baler combination for a selected range of crop densities, combine header widths (crop density x header width = swath density) and chosen field slope, for the transmission gear engaged, and presents the results in graphical form. When the upper limit of the selected swath density range is attained, or the pre-set engine load limit is exceeded, the simulation automatically increments the gear selection and repeats the calculations.

   29 Workrate is defined in terms of the crop tonnage baled per hour (mass flowrate through the baler): in level field conditions the baler torque requirement, via the PTO, is the main source of engine loading.

   The specific actions performed by the model are as follows:

   i) the values of crop density, header width and field slope are selected ii) the model is initiated under the following conditions:

   - transmission gear = B1 - forward velocity = unknown - no-load engine speed = 2120 erpin (1000 PTO rpm) - swath density = minimum of selected range iii) the model then proceeds through an iterative process to converge on the steady state engine speed, and therefore forward velocity, which satisfies the calculated loading under initialised conditions iv) the value of swath density is incremented and the iterative process repeated v) the calculations are repeated until either the maximum swath density is reached or the engine is overloaded, at which point the 25 transmission gear is incremented and the swath density range reset to the lower limit As seen from a typical output of the simulation, shown in Figure 7, at lower end of the swath density range the theoretical workrate increases as the transmission gear increments. This is as would be expected, due to the associated increase in forward speed. However, above swath densities of 3.5 kg/m the torque output of the tractor engine becomes limiting in successive gears. The increased curvature at the upper limit of each transmission gear plot is due to the more rapid reduction in engine speed as the loading on the engine mcr.eases beyond the governor line and the engine speed reduces along the maximum torque curve.

   As can be seen from Figure 8, the proportion of engine output utilised by the baler varies considerably over the range of field slope displayed. On a level field with the given swath density, over 80% of the power demand on the tractor originates from the baler via the PTO shaft. However, if the slope of the field increases above 15' then the majority of the power output of the tractor is required to overcome field slope and rolling resistance, via the transmission, axles and tyres. The limiting factor of field slope on the theoretical maximum workrate is also demonstrated: the tractor and baler. could satisfactorily operate in gear B4 on a level field, but the engine would be overloaded, necessitating a down change, if the field slope increased above 10'.

   Although not shown as an input to the reference model of Figure 6 or the method steps of Figure 4, an optional feature of the invention is a farther sensor, that may be mounted as illustrated schematically by reference numeral 37 at the front of tractor 10, for the purpose of detecting heaps in the swaths.

   Heap sensor 37 may include a mechanical probe connected to a transducer, the probe being moveable on contact with a swath heap to cause the transducer to generate a swath signal. The transducer may be operatively connected to one or more of the microprocessors 29, eg. via CAN-BUS 31.

   31 Alternatively heap sensor 37 may be an optosensor or a radar or an ultrasound sensor, for example.

   The output signal from the heap sensor may for example trigger the calling of a subroutine that causes rapid decrementing of the transmission ratio temporarily to reduce the forward speed of the tractor/baler combination so that the precompression chamber does not become clogged by the straw in the swath heap.

   32 CLAIMS 1. A method of controlling a tractor/baler combination comprising the steps of:

   (i) advancing a tractor/baler combination through a swath or windrow of biological matter with the tractor PTO operating at a generally constant speed to power the baler and the baler operating to take up biological matter; (ii) during step (i) assessing the flowrate of biological matter in the baler; (iii) comparing the assessed flowrate with an optimal flowrate; and (iv) if the assessed flowrate differs from the optimal flowrate by more than a predetermined amount, changing the speed of advancement of the tractor/baler combination, and hence changing the flowrate of biological matter in the baler.

   2. A method according to Claim I wherein the step of changing the speed of advancement includes the step of:

   (iv a) shifting the tractor transmission by one or more increments or decrements.

   3. A method according to Claim 2 wherein the step of shifting the tractor transmission includes incrementing the tractor transmission ratio if the assessed flowrate is less than an optimal flowrate by more than a first said predetermined amount; and decrementing the tractor transmission ratio if the assessed flowrate is more than an optimal flowrate by more than a second said predetermined amount.

   4. A method according to any preceding claim wherein the tractor 33 engine speed is maintained generally constant during advancing of the tractor/baler combination.

   5. A method according to any preceding claim wherein the step of 5 assessing the flowrate includes:

   (v) periodically detecting one or more of. the baler packer or rotary feeder driveshaft torque; the tractor power take-off (PTO) shaft torque; the baler packer fork con rod force; and the position of a sensor door in a pre-compression chamber of the baler; (vi) generating a signal indicative thereof that is proportional to the said assessed flowrate; and (vii) using the said signal, to compare the assessed flowrate against the optimal flowrate.

   6. A method according to any preceding claim wherein when the step (iii), of comparing the assessed flowrate with the optimal flowrate, indicates that the assessed flowrate is less than the optimal flowrate by more than the first predetermined amount, the method includes the steps of:

   (vii) predicting the load on the tractor engine in the event of incrementing of the tractor transmission ratio by one ratio increment, and (ix) only incrementing the said transmission ratio if the predicted load is less than a predetermined maximum.

   7. A method according to Claim 6 wherein the step (vii), of predicting the load on the tractor engine includes the sub-steps of:

   (viii a) assessing the engine torque and generating a signal indicative thereof, and 34 (viii b) inputting the resulting engine torque signal into a reference model, whereby to permit the said prediction.

   8. A method according to Claim 7 wherein the step (viii a) of assessing the engine torque includes operating a torque sensor operatively connected to or forming part of a tractor engine flywheel.

   9. A method according to any of Claims 6 to 8 wherein the step (viii), of predicting the load on the tractor engine, is carried out a plurality of times and wherein the said transmission ratio is incremented only if a predetermined number of consecutively predicted loads in less than the said predetermined maximum.

   10. A method according to Claim 3 or any claim dependent therefrom wherein the step (iii) is carried out a plurality of times and wherein the said transmission ratio is decremented only if a further predetermined member of consecutive said assessments indicates a need to decrement the transmission ratio.

   M 11. A method according to Claim 10 wherein when the step (iii) indicates that the assessed flowrate is greater than the optimal flowrate by a said second predetermined amount the further predetermined number of consecutive said assessments is greater than when the assessed flowrate is greater than the optimal flowrate by a further predetermined amount, that is greater than the second predetermined amount.

   12. A method according to Claim 2 or any claim dependent therefrom, wherein incrementing and decrementing of the transmission ratio take place when the reciprocably moveable baler plunger occupies a predetermined position in its reciprocal movement.

   13. A method according to any preceding claim when co-ordinated by a programma le processor operatively connected to receive and process signals indicative of one or more of:

   the baler packer or rotary feeder driveshaft torque; the tractor power take-off (]PTO) shaft torque; the baler packer fork con rod force; and the position of a sensor door in a pre-compression chamber of the baler; and the tractor transmission ratio.

   14. A method according to Claim 13 wherein the processor continuously detects signals indicative of one or more of the said tractor PTO shaft torque and the tractor engine torque and processes the resulting values corresponding to a predetermined part of the plunger cycle.

   15. A method according to Claim 13 or Claim 14 wherein the said processor continuously detects signals indicative of one or more of the said tractor PTO shaft torque and the tractor engine torque and averages the resulting values over a cycle of the baler plunger.

   16. A method according to any of Claims 13 to 15 wherein the said processor maintains the tractor engine speed generally constant, regardless of the engine loading.

   17. A method according to Claim 13 wherein the programmable processor includes or is operatively connected to a memory having for comparison purposes one or more said optimal flowrate values.

   18. A method according to any of Claims 13 to 16 when dependent 36 from Claim 12, wherein the programmable processor includes or is operatively connected to one or more devices having stored therein for comparison purposes said first, second and further predetermined amounts, said predetermined maxima and the predetermined position of 5 the baler plunger.

   19. A method generally as herein described, with reference to and/or as illustrated in the accompanying drawings.

   20. A tractor/baler combination including a programmable processor, and operatively connected thereto one or more sensors detecting one or more of the baler packer or rotary feeder driveshaft torque; the tractor power take-off (PTO) shaft torque; the baler packer fork con rod force; the position of a sensor door in a pre-compression chamber of the baler; and the tractor transmission ratio the programmable device being programmed to carry out a method according to any preceding claim in dependence on the output of one or more said sensors.

   21. A tractor/baler combination according to Claim 20 including a baler packer driveshaft torque sensor including a strain gauge operatively connected to the packer or rotary cutter driveshaft and connected in a bridge circuit.

   22. A tractor/baler combination according to Claim 20 including a torque sensor for detecting the PTO shaft torque.

   37 23. A tractor/baler combination according to Claim 20 including a packer fork conrod force sensor including a strain gauge operatively connected to the packer conrod and connected in a bridge circuit.

   24. A tractor/baler combination according to Claim 20 including a sensor door position detector including an LVDT operatively connected to generate a signal indicative of the position of the said sensor door.

   25. A tractor/baler combination according to any of Claims 20 to 25 including, at a location in front of the baler precompression chamber, a swath heap sensor that generates a signal indicative of a swath heap, the programmable device being programmed to reduce the speed of advancing of the combination on generation of a said swath heap signal.

   26. A tractor/baler combination according to any of Claims 20 to 25 including a baler plunger. position sensor that generates a signal indicative of the position of the baler plunger, the baler plunger position sensor being operatively connected to feed the said position signal to the programmable device.

   27. A tractor/baler combination according to any of Claims 20 to 26 wherein the programmable processor includes or is operatively connected to a memory having for comparison purposes one or more said optimal flowrate values.

   28. A tractor/baler combination according to any of Claims 20 to 27 wherein the programmable device includes or is operatively connected to one or more devices having stored therein for comparison purposes said first, second and further predetermined amounts, said predetermined maxima and the predetermined position of the baler plunger.

   38 29. A tractor/baler combination according to any of Claims 20 to 28 including an inclinometer that generates an inclination signal indicative of when the said combination is ascending or descending a slope, the inclination signal being input to the programmable processor.

   30. A tractor/baler combination according to any of Claims 20 to 29 including a means for detecting for determining the rolling resistance of the said combination and generating a rolling resistance signal indicative thereof, the rolling resistance signal being input to the programmable processor.

   31. A tractor/baler combination according to any of Claims 20 to 30 wherein the programmable processor is or includes one or more microprocessors.

   32. A tractor/baler combination according to any of Claims 20 to 31 wherein the programmable processor includes or is operatively connected to a memory having stored therein a steady state reference model predictive of the behaviour of the tractor/baler combination for variations in one or more of:

   the transmission ratio of the tractor; the density of the swaths through which the tractor/baler advances; and the inclination of any of a -range of slopes up or down which the said combination advances.

   33. A tractor/baler combination generally as herein described, with reference to and/or as illustrated in the accompanying drawings.

   39 An I Amendments to the claims have been filed as follows I A method of controlling a tractor/baler combination comprising the steps of:

   (1) advancing a tractor/baler combination through a swath or windrow of biological matter with the tractor PTO operating at a generally constant speed to power the baler and the baler operating to take up biological matter; (ii) during step (i) assessing the flowrate of biological matter in the baler; (iii) comparing the assessed flowrate with an optimal flowrate; and (iv) if the assessed flowrate differs from the optimal flowrate by more than a predetermined amount, changing the speed of advancement of the tractor/baler combination, and hence changing the flowrate of biological matter in the baler.

   2. A method according to Claim 1 wherein the step of changing the speed of advancement includes the step of:

   (iv a) shifting the tractor transmission by one or more increments or decrements.

   3. A method according to Claim 2 wherein the step of shifting the tractor transmission includes incrementing the tractor transmission ratio if the assessed flowrate is less than an optimal flowrate by more than a first said predetermined amount; and decrementing the tractor transmission ratio if the assessed flowrate is more than an optimal flowrate by more than a second said predetermined amount.

   4.A method according to any preceding claim wherein the tractor engine speed is maintained generally constant during advancinY- of the 1 1 0 tractor/baler combination.

   5. A method according to any preceding claim wherein the step of assessing the flowrate includes:

   (v) periodically detecting one or more of: the baler packer or rotary feeder driveshaft torque; the tractor power take-off (PTO) shaft torque; the baler packer fork con rod force; and the position of a sensor door in a pre-compression chamber of the baler; (vi) generating a signal indicative thereof that is proportional to the said assessed flowrate; and (vii) using the said signal, to compare the assessed flowrate against the optimal flowrate.

   6. A method according to any preceding claim wherein.when the step (iii), of comparing the assessed flowrate with the optimal flowrate, indicates that the assessed flowrate is less than the optimal flowrate by more than the first predetermined amount, the method includes the steps of:

   (viii) predicting the load on the tractor engine in the event of incrementing of the tractor transmission ratio by one ratio increment, and (ix) only incrementing the said transmission ratio if the predicted load is less than a predetermined maximum.

   7. A method according to Claim 6 wherein the step (viii), of predicting the load on the tractor engine includes the sub-steps of:

   (viii a) assessing the engine torque and generating a signal indicative thereof, and (viii b) inputting the resulting engine torque signal into a - c.. rence model, whereby to permit the said prediction.

   8. A method according to Claim 7 wherein the step (viii a) of assessing the engine torque includes operating a torque sensor operatively connected to or forming part of a tractor engine flywheel.

   9. A method according to any of Claims 6 to 8 wherein the step (viii), of predicting the load on the tractor engine, is carried out a plurality of times and wherein the said transmission ratio is incremented only if a predetermined number of consecutively predicted loads is less than the said predetermined maximum.

   10. A method according to Claim 3 or any claim dependent therefrom whereinthe step (iii) is carried out a plurality of times and wherein the said transmission ratio is decremented only if a farther predetermined member of consecutive said assessments indicates a need. to decrement the transmission ratio.

   11. A method according to Claim 10 wherein when the step (iii) indicates that the assessed flowrate is greater than the optimal flowrate by a said second predetermined amount the further predetermined numberof consecutive said assessments is greater than when the assessed flowrate is greater than the optimal flowrate by a further predetermined amount, that is greater than the second predetermined amount.

   12. A method according to Claim 2 or any claim dependent therefrom, wherein incrementing and decrementing of the transmission ratio take place when the reciprocably moveable baler plunger occupies a predetermined position in its reciprocal movement.

   43.:..0:. 0..:

   13. A method according to any preceding claim when co-ordindted by a programmable processor operatively connected to recei-,,-: ind process signals indicative of one or more of:

   the baler packer or rotary feeder driveshaft torque; the tractor power take-off (PTO) shaft torque; the baler packer fork con rod force; and the position of a sensor door in a pre-compression chamber of the baler; and the tractor transmission ratio.

   14. A method according to Claim 13 wherein the processor continuously detects signals indicative of one or more of the said sensor door position, tractor PTO shaft torque and tractor engine torque and processes the resulting values corresponding to a predetermined part of the plunger cycle.

   15. A method according to Claim 13 or Claim 14 wherein the said processor continuously detects signals indicative of one or more of the said sensor door position, tractor PTO shaft torque and tractor engine torque and averages the resulting values over a cycle of the baler plunger.

   16. A method according to any of Claims 13 to 15 wherein the said processor maintains the tractor engine speed generally constant, regardless of the engine loading.

   17. A method according to Claim 13 wherein the programmable processor includes or is operatively connected to a memory having for comparison purposes one or more said optimal flowrate values.

   18. A method according to any of Claims 13 to 16 when dependent lk_ from Claim 12, wherein the programmable processor includes or is operatively connected to one or more devices having stored therein for comparison purposes said first, second and further predetermined amounts, said predetermined maxima and the predetermined position of the baler plunger.

   19. A method generally as herein described, with reference to and/or as illustrated in the accompanying drawings.

   20. A tractor/baler combination including a programmable processor, and operatively connected thereto one or more sensors detecting one or more of the baler packer or rotary feeder driveshaft torque; the tractor power take-off (PTO) shaft torque; the baler packer fork con rod force; the position of a sensor door in a pre-compression chamber of the baler; and the tractor transmission ratio the programmable device being programmed to carry out a method according to any preceding claim in dependence on the output of one or more said sensors.

   21. A tractor/baler combination according to Claim 20 including a baler packer driveshaft torque sensor including a strain gauge operatively connected to the packer or rotary cutter driveshaft and connected in a bridge circuit.

   22. A tractor/baler combination according to Claim 20 includi g a torque sensor for detecting the PTO shaft torque.

   23. A tractor/baler combination according to Claim 20 including a packer fork conrod torce sensor including a strain gauge operatively connected to the packer conrod and connected in a bridge circuit.

   2 4. A tractorIbaler combination according to Claim 20 including a sensor door position detector including an LVDT operatively connected to generate a signal indicative of the position of the said sensor door.

   25. A tractor/baler combination according to any of Claims 20 to 25 including, at a location in front of the baler precompression chamber, a swath heap sensor that generates a signal indicative of a swath heap, the programmable device being programmed to reduce the speed of advancing of the combination on generation of a said swath heap signal.

   is 26. A tractor/baler combination according to any of Claims 20 to 25 including a baler plunger position sensor that generates a signal indicative of the position of the baler plunger, the baler plunger position sensor being operatively connected to feed the said position signal to the programmable device.

   27. A tractor/baler combination according to any of Claims 20 to 26 wherein the programmable processor includes or is operatively connected to a memory having for comparison purposes one or more said optimal flowrate values.

   28. A tractor/baler combination according to any of Claims 20 to 27 wherein the programmable device includes or is operatively connected to one or more devices having stored therein for comparison purposes said first, second and further predetermined amounts, said predetermined maxima and the predetermined position of the baler plunger.

   A tractor/baler combination according to any of Claims 20 to 28 including an inclinometer that generates an inclination signal indicative of when the said combination is ascending or descending a slope, the inclination signal being input to the programmable processor.

   30. A tractor/baler combination according to any of Claims 20 to 29 including a means for detecting and/or determining the rolling resistance of the said combination and generating a rolling resistance signal indicative thereof, the rolling resistance signal being input to the programmable processor.

   31. A tractor/baler combination according to any of Claims 20 to 30 wherein the programmable processor is or includes one or more microprocessors.

   32. A tractor/baler combination according to any of Claims 20 to 31 wherein the programmable processor includes or is operatively connected to a memory having stored therein a steady state reference model predictive of the behaviour of the tractor/baler combination for variations in one or more of:

   the transmission ratio of the tractor; the density of the swaths through which the tractor/baler advances; and the inclination of any of a range of slopes up or down which the said combination advances.

   33. A tractor/baler combination generally as herein described, with reference to and/or as illustrated in the accompanying drawings.